Age hardening austenitic steel



Aug. 5, 1952 PAYSQN 2,606,113

AGE HARDENING AUSTENITIC STEEL Filed Dec. 20, 1947 BAR 51 75- 16C; 25.0 NI; 20.8 ca 5.5 AL.

OLUTION TREATED 2200 F.

Aemc TIME HOURS 3 BAR sue-25c; 24.5 m; ZLBCR; 3.5AL;2.6M0.

SOLUTION Trzezn-rso 2300FI .2 .5 1.0 2 4- 8 IO 20 3O 50 200 400 AGING TIM s- Hour-2s INVENTOR.

PETER PAYSON.

ATTORNEYS.

the analysis, by heat: treatment at Patented Aug. 5, 1952 1 ,derl saiiqn l s e This invention pertainsto hardenabla-cor- :rosion and heat-resisting austenitic steels, and

more particularly to a steel of this character which. c nbeiorged and. rolled. a d'which. as annealed or solution-treated, isgq'ulte soft so thatit. can be. cold-romedreadih, o ma hine tly be. hardened .110 dependin upon relatively low and which can subseque Rockwell C 30.01 40, or higher,

temperatures.

The essentially stainless steels, such as A. I. S. I. types 410, 420 and-440,1 e., ,those containing. aboutj12; e:l% chromium carbon. about. 0.1 to ,1 or I the chromium-moire]; steeltype 4131 containin about 16% chromium, 2% nickel and 0;]; to 0.2% .0341- bon, have to be treated to temperatures in excess of 17.0.0 E. as axnecessarr s tor hardening. This geneIaIlyentails-serious oxidation or discoloration of the surface, req fring final cleaning and polishing to; confer the desired metallic, lusterand corrosion-resistance to articles made therefrom. These steels harden by martensite rorrnation, and the hardening thereof without discolorationmust be effected incspecial atmosphere furnaces, which are ordinarily not readily available; Furthermore; even the best Iof these steels, when properly heath-treated and polished, ha've'limited, resistance to corrosion; as indicated for example in the 20% sodium ch19.-

ride spray test. 1 The austenitic. stainless, steels of which A. I. :S. I. types 302, 310:and 316 are examples, 1, -e.,

18-8, 25-20 and 18-12 with molybdenum. respectively, when in the annealed or solution-treated condition, are easy to cold-work and machine, but they can behardened onlyby severe cold-rollin er; drawing. operations. Articles of a preciable strengthiand, wear-resistance can therefore be made ironi these steels only in simple sections which can be cold-rolled or cold drawn. These steels, which are highly resistant to. corrosion aswell as to oxidation at high temperatures, are therefore limited in their usefulnessfor articles 'or high strength, v

Steels are known, a for examblethose destraight chromiumhardenable 1 Molybdenum an Peter li'ayson', New York, Nuyfflasgjgnqnm Cub e SteeLCompa-ny of Am ri New N. Y., a corporati n of New-Jets I ,y

20, 7"; Se iam 1132.329,

zoiaiins. (01.754 in scribed? in French Patent 743,179, which are stainlessand"hardenableltoan appreciable degree by a heat treatment causing a phase change 1mm unstab ehust niteto gmartensiter But-such s e s h ve; the disadvantag that th y are. no r adilycrkablejhyeold-io e ne c t-mach nin since; hens ,orderlinealloys, they tend, to harden by: martensite iormation while. they-are being worked. A Other stainless steelsare known, as 0.51?

xample those described in-U. SQBate tTZBfiA-l r which hardenapnreciably by aeineof stress-- laden ierrite ,suchsteelsalso havethe disad vanta e ment on d aboveo-f not, be n readily worka le because they ar ,zfairlhr ard, ab ut Rockwell "0? 2.3,.nripr to the aging treatment. Final y, therearek own stainless steels of sumcient. alloy-content to; be substantially austenitic, and which may. be harden d s mewhat by aging ,withoutany' change. from austemte to the ferritiqphasef 'Howeyen the known. ste ls Qt th s type do h rde jsumci ntly t te oi appreciable us inindust Now'lhare dissio ere;

y Y a 'in'aecordanoe w th the nresentinrentio that re are. eer-ta n steel composit o s-which. by .rtue or the balanee oiniclke chromiumrand and in some analyses also mol bden l present in the s e havea soft, ductile and. substantially aus e itic structure, as annealed r so 'r re an whichundergo a marked ase in ardn H or softer, to Rockwen 3 or so or h den y an a i eatn; at bout 1100 to 1400," without the formation o ma nsite r any ther rer-ritic produ r mthe u te'nites ee sw ih I av these p operties, are

discov re t p ss those within the following ,raneeor analys sgh nsti utinethe broad range o ana ysis Qrmy e on. viz:

Manganese nickel About 20 to 30% Chromium "About 15 to 25% Aluminum About 2.5 to 4.5%

d/or t ngsten Upto about 5%- Substantially iron Balance 3 It will be understood that by specifying the balance as substantially iron is meant iron containing the usual amounts of silicon and residual elements ordinarily found in high quality steel. The preferred composition for one of the lower cost varieties of this steel is:

Carbon About .10 to 25% Manganese About 1.0 to 2.0% Silicon About .20 to 50% Nickel About 22 to 2 Chromium About 20 to 22% Aluminum About 3 to 4% Balance Substantially iron And for a steel which attains a somewhat higher hardness, and which has better corrosion resistance, and better strength at elevated temper- Balance Substantially f iron These steels can be hardene d respectively from Rockwell 1'13 83 {as jsoliition treatedat 2200f E, to Rockwell 40as a'ged'at1300f 1i". for8hours; and from Rockwell "B .87 as solution treated at 2300 F., to Rockwell C 4 3 as aged at'1400 F. forv 8 hours. The maximum hardnesses attainable are evenhigher for longer aging times and somewhat lower agingtemperatures. That this hardening is strictly age'hardening without phase change is substantiate'd by. theffacts that the changes in hardness with time and temperature of aging as shown in Figures 1 and 2 of the ac- 'companyingdrawing, followthe classic pattern for age hardening alloys discussed'byE'. S; Davenport and E. C. Bain in the article The Aging of Steel in Transactions of the American Society for Metals, volume 23, 1935, pages'1047 to 1096; and that the steel remain? substantially nonmagnetic after the hardening: is completed.

The, balance in relative proportions of the variouselements aforesaid in. the steel of the I invention, is quite important for the production of the desired forgeable, corrosion and heat re sisting properties, including asoft and substantially-austenitic structure as solution treated, but

which can be hardened appreciably by aging at a relatively low temperature. increased, the forgeability 7 decreases anci the aforesaid high nickel, chromium, aluminum, molybdenum analyses become practically non- As the carbonis' 6 TABLE 1 .--NON-AUSTENITIC Ni-Cr-Al STEELS Bar 0 Mn 81 Ni Or A] .10 1. 43 3O 14. 66 18. 36 3.10 08 1. 41 39 17. 55 18. G 3. 15 1. 33 44 14. 19 20. 24 3. 70 14 1. 37 49 18. 86 20. 52 3. 75 15 1. 41 55 20. 45 20. 25 3. 57 13 1.46 50 14. 53 22. 52 3. 6O .14 1.48 .54 .04 22.60 3.53

On the other hand, when the nickel lus manganese content is above that of the chromium contentnthe .steels withhigh aluminum content are} substantially non-magnetic: or austenitic. Examples of such steels are given in Tables 2 to 10.

1n the substantially austenitic nickel-chromium-aluminum steels, there is a minimum amount of aluminum; required to confer appreciable ;hardening .of. the-steel by aging, as shown in Table 2." I

" *ra'B' n a snns'rAN'rrALLY AUSTENITIC Ni-CrAl STEELS vEyes-t of Al content on hardening by aging [Samples solution trc'a'ted'at 2100 F. and aged atl300fF or 16 hours forgeable when the carbon isover about 0.40%.

Forgeability is also rapidly impaired aslthe aluminum content exceeds about 4.5 %.and the molybdenum content exceeds about 15.0 When steels of the general type aforesaid contain appreciable amounts of aluminum, they are strongly mag-'- netic, that is, not substantially austenitic as .is desired in steels that are easy to cold-work, if the'nickel plus manganese content is below, that of the chromium content. For example, the steels shown in Table 1 were definitely-magnetic as solution treated at 2100 F. A

- Per- "Per- Per- Pcr- Percent Percent Rockwell Bar cent cent can v; a cent v G MD Si I 1x1 r A} Hardness 8778 .11 1.48 .42 23.47 18.48 1.00 B 84 8779 .11 l. 47 29 i 23. 47' 18. 67 1. 98 C 7 .11 1. 51 .36 22. 73 18.30 2.56 C 23 .10 1. 36 .39 23.17 19.00 8.10 C 33 .12 1. 45 31 25. 83 18. 06 4. 36 C 38 Also in the substantially auste'nitic steels containing aluminum, the degree of age hardening is dependent on the chromium content as is shown in Table 3(.

a Per- Per- Per- Per- Per- Per Per- Bar cent cent cent cent cent cent cent g g 0 Mn Si Ni' O: n Mo 8838- 10 1. 46 39 23.19 15. 57 2. 92 C 24 S613 10 1. 36 39 23. 17 19.00. 3. 1U C 33 .8839- 10 1. 5O 39 22. 73 21. 05 3. 09 C 38 5230 .17 1. 35 49 22. 79 21. 03 3. 44 C 38 5007. OS 1. 39 47 21. 29 16. 37 3. 14 C 24 5003- 10 1. 49 43 24. O6 19. 21 3. 17 C 31 5009 10 v 1.. 49 42 23. 66 19. 78 3. 35 C 34 5010- 12 1. 53 45 24.,52 I 22. 07, 3. 30 G 36 .5016- 11 1. 52 36' 25. 61 16. 33 3. 76 C 32 5012- 09 1. 46; 45 25. 30 18. 39, 3. 65 C 37 5017- 11 1.53 .33 25. 37 20. 16 a. 74 c 40 These data show that attainable hardness by aging increases with increasing chromium. HownaErmaTANm Y .mwm

I 33355310 content harrieqn'ng 33mg "317333 of Mo 36115311053 53133551355 aging 5 v [Samples solution treated at 2300 F. nd aged at 1400 [Samplessolutiontreatedat2300F.211dag0datl400FJor ifi-hoursl a w 1 l 3 Per- Per- Per- Per- Per- Per- Per- 1 i761" r e P91- 9 .3 R k 119 Rockwell -Ba1- cent cent cent cent cent cent cent we i? 1122 3? 1 0% it o Hardness M .0 r 41 M Ha'dm 884G L45 '32 253! A9 2.63 C23 5053. 09 1.42 .33 24.34 20.00 3.61 2.77 40 3347. .11 1.41 .35 25.33 19.12 2.76 2. 034 5177- 24-72 151 37 3343. .12 1.41 .41 25.43 13.46 2.65 6.54 -042 517831425 L37 10195 43 my .14 M4 '34 2M7 18,36 Z79 047 5179. .33 1.37 .53 24.53 .2125 3.49 2.53 41 3354. .13 .1.50 .35 23.50 19.93 3.36 0.27.15... 3355. .15 1.40 .35 23.01 13.50 3.01 5.10 I I 322$. :ti ti? 1% 33:13 i??? 3:33 2:3? 33. Th e i ofihesesteelsisy e em fected by carbon content, particularly in the "jlst'eels containing molybdenum, and is progres siv'ely worse with increasing carbon. Whenthe It is shown above that the attainable hardness carbon-is over aboutj0.40%, the steel is'hardly by aging increases with increasing molybdenum. forgeable. Y However, it has been found that the 'forgeabllity Finally, the effect of increasing nickel above decreases also with increasing molybdenum, and about 30.0% is generally to decrease the hardness steels with more than about 5.0% molybdenum attainable by aging in these steels, as shownin can be forged only with difilculty, and those with the following Table 7.. v molybdenum around 10% can be forged-hardly Y at all. Q j' TABLE 7.-SUBSTAN'IIAI.LY AUSTENITlIC The efiect of carbon on the attainable hardness Ni- -C I-T-A1 S I'EELS by aging is practically negligible as shown in the 7 4 u following Tables 5 and 6. Efiect 0f N1 content on hardening by agmg.

I [Samples solution treated at 2100 F. and aged at 1300 3:." F.'f0r16l1ours] TABLE 5.--SUBS TANTI ALL AUSTENITIC y 1 NiCr---A1STEELS- Per- Per- Per- P Per cent cent Gent ercent Percent cent RoekwellO Mn N1 Qr...- H aran s Efiect ofCcontent on hardeningby aging 1 Sam les solutibn treated at 2200 I3. and aged-at '130 4 I t p F.,for 16 hours] I .35 29.04 19.06 29 I 1 I I .31 31.72 13.63 22 Per- Per: Per Per Per- Per- I h 1 RockwellC v t 1 t I BM 13 3? 151 a i Hardness The temperature for annealing or solut1on xy treating' these substantially austenitic nickel- .10 1.23 .50 24.70 20.04 3.13 .3. hm f i f y Steels y be betweenabout 1900 and 2400 F. but preferably I09 1123 I54 24. 00 20170 3141 40 between 2100 and 2300 F., the steels containing .16 1.34 .55 24.97 20.34 3.52 .42 1. 24 L26 .53 2537 mm H5 39 v.molybdenumrequiring the higher temperatures. ,5 24 9s ,8 ,6 4 --'I'he eiTect-of solution temperature on the hard- M30 24-58 21-18 ness as annealed and after aging is shown in the following Table 8.

TABLE 8.-.-SUB STANTIALLY AUS'IENITIC Ni- Cr--Al S 'I'EELS Efiect of solution treatment on hardness before and after aging [Samples solution treated 31' 1900to F. and aged for 18 hours at :1350 3.1.

Rockwell Hardness." Percent in Ber As Solution.TreatedF. As Aged F. 0 Ni or A1 1900 2000 2100 2200 2300 1900 2000 2100 5056 --.09 24.3 20.0 3.6 2.3 1392' B90 B33 B B80 037 040 641 13.42.3143 5057.. .09 24.9 20.5 3.4 3.0 1396 B91 B89 B37 B37 039 043- 043 043 045 5096.. .09 25.9 22.7 3.2 2.3 1195 B B33 B88 B33 040- 042 042- 042 042 5053.. .09 27.4 20.9 3.2 23 B80 B79 B78 B75 B72 C37 033 '039 C39 0,41 5050.. .09 23.0 20.1 3.3 3.7 B33. B30 B79 B77 B74 C39 e40 041 041" 043 5050 .10 23.1 23.2 3.2 2.3 0 21 1392 B88 33 33 040 041 042. 0 3- Q43 2,eoc,1 1a: 7

The best aging treatments for these steels is 2 to 4% of metal of the group molybdenum and between about 12001111111 1500 F., the molyb tungsten; about 0.1 to 0.2'5i%'ca1'-bon; an'dztheibaldenum steels requiring a somewhat higher temance substantially'all111311;? V perature than the steels without molybdenum, 2. A Iorgeable and machinable, age hardening,

' 5 heat and corroslon reslsting alloy steel. characas shown in the'following Table 9.

I TABLE. a- SUBSTANTIALLY AUS'I'ENI'I'IC NiCr'Al--Mo S'I'EELS Eflect of solution and aging treatments on at- Y tainable hardness [Rockwell hardnesst "C ercept as indicated] -js01. 'rr. at 2100 F; s 1; Tnst F; s01. Tr. at 2300 F; raging aged ataged zit-'- aged at- 1200 1300 1400 1500 12003 1aoo 1400 150o 1200 1300" 1400 1500 Both- Tables 8 and 9 emphasize the'truly reterized in being ductile, substantially austenitic markable degree to which these properly baland having a hardness below about 3" 90 Rockanoed steels harden by aging. well, as solution treated at about 1900 to 2400 F.,'

That these steels 1 asiaged are really high and in being hardenable in excess 'of "0 30 Rockstrength corrosion resistant materials are eviwell on subsequent aging at about 1100 to 1500 denced by the mechanical properties---data--in- F., said steel containing: about Zeta 26% nickel; Table 10, and by the fact that as age hardened; about 1 to 2% manganese; about 19 to 21% these steels are equivalent tov thew'ell known 18-8 chromium; about 3fto 4%- aluminum; about 2 to Stainless Steel, as annealed in corrosion re 4% molybdenurn; about 0.1 to 0.25% carbon; and sistance to a spray made up of 20% sodium the balance substantially all iron. chloride. l PETER PAYSQN.

TABLE 10;SUBSTANTIALLY AUSTENITIC Ni-Cr-A1STEELS I Mechanical properties of aged steels Teste d as standard .505 tensile pieces and V-notch Izod pieces] Percent I I I T 8 Y8 B31 Treatment c p.11. it 15 2.1. pi zr e t 3512310 15. 35 5.

0 Ni Gr Al 5172 .00 24.0 20.7 s7 170,000 115,000 13.6 24.4 11 5173 .16 25.0 20.8 as 150,000 112,000 15.0 23.4 0 5727 17 22 s 21 o a 4 {monwatr As shown by the test results above presented, the steel of the invention will ordinarily contain REFERENCES CITED about 20 to 3o%rmckel; together w about The following references are of record in the to 5% manganese, the other constituents being file of thls'patenh as above set forth. W UNITED STATES PATENTS 10194111.? Number Name Date .AIQ BFF P a machinable ehe m 1 941 648 Armstrong J an 2 1934 heat and corrosion-resistin alloy steel, charac-' T, 2 048 1 7 I pining J l 1936 i i 3 being ductile, substantially austeniflc -212001208 Parsons May 7 1940 and having a hardness below about B 90 Rock- 2,381,416 Wyche et 1945 well, as solution treated at about 1900 to 2400" F., 7 e and in being hardenable in excess of C 30 1 i FOREIGN PATENTS Rockwell on subsequent aging at about 1100 to Number Country Date 1500 F., said steel containing: about 24 to26%" 136,661 7 Austria Oct. 15, 1933 nickel; about 1 to 2% manganese; about 19 to" 743,179 France Mar. 25, 1933 21% chromium; about 3 to 4% aluminum; about 371,334 Great Britain Apr. 13, 1932 

1. A FORGEABLE AND MACHINABLE, AGE HARDENING, HEAT AND CORROSION-RESISTING ALLOY STEEL, CHARACTERIZED IN BEING DUCTILE, SUBSTANTIALLY AUSTENITIC AND HAVING A HARDNESS BELOW ABOUT "B" 90 ROCKWELL, AS SOLUTION TREATED AT ABOUT 1900 TO 2400* F., AND IN BEING HARDENABLE IN EXCESS OF "C" 30 ROCKWELL ON SUBSEQUENT AGING AT ABOUT 1100 TO 1500* F., SAID STEEL CONTAINING: ABOUT 24 TO 26% NICKEL; ABOUT 1 TO 2% MANGANESE; ABOUT 19 TO 21% CHROMIUM; ABOUT 3 TO 4% ALUMINUM; ABOUT 2 TO 4% OF METAL OF THE GROUP MOLYBDENUM AND TUNGSTEN; ABOUT 0.1 TO 0.25% CARBON; AND THE BALANCE SUBSTANTIALLY ALL IRON. 